Topic 8

Question 1

what is meant by enthalpy

Answer 1

The total chemical energy inside a substance

Question 2

For an Exothermic reaction what is the enthalpy change

Answer 2

negative

Question 3

For an endothermic reaction what is the enthalpy change

Answer 3

Posistive

Question 4

what is standard enthalpy change of reaction

Answer 4

Chnage which occurs when equation quantites of material react under standard conditions & with everything in it’s standard state

Question 5

what is standard enthalpy change of formation

Answer 5

Enthalpy change when one mole of a compound is formed from its elements under standard conditions.

Question 6

what is standard enthalphy change of combustion

Answer 6

Enthalpy change when one mole of a compound burns completely in oxygen under standard conditions.

Question 7

what is standard enthalpy change of neutralisation

Answer 7

Enthalpy change when the acid and alkali in the reaction neutralise each other in standardised conditions to form 1 mole of water.

Question 8

what is bond dissassociation enthalpy

Answer 8

Enthalpy change when a covalent bond is broken with all species being in gaseous state

Question 9

what is mean bond enthalpy

Answer 9

Enthalpy change when 1 mole of a covalent bond is broken & averaged over range of molecules

Question 10

what is Hess’s Law

Answer 10

Enthalpy change of a chemical reaction at constant pressure is dependant of the route taken & depends on the initial & final states

Question 11

what can we do to test if the cycles are correct

Answer 11

• Start anywhere on the cycle & add any number until you reach where you were
• If you go against the arrow switch the sign
• If correct it should be equal to zero